IEP of carrageen?

[Kaiser]

Does anyone have a source for the isoelectric point of carrageen? (Irish Moss) I spent almost all day searching the web but only found the IEPs of gelatin. I need this for an article.

Kai

 

[pjj2ba]

Hmmm, I never really thought of an IEP for anything but proteins (having mixes of positive and negative charges). A quick look in my favorite ref doesn't give one, but it does say "precipitates proteins where the pH of the soln is below the isoelectric point of the protein. The majority of proteins in a barley seed will have a IEP over that of typical mash pH. Of course the malting process and the mash itself will result in a lot of protein cleavage that will change the IEP of the resulting peptides and I can imagine that some might then be below ~5.5.

Also found this in a book. It says that carrageenan is strongly negatively charged over the entire pH-range encountered in food.
Nice tidbits in a marine book

I'm thinking it has more to do with ionization of the sulfate groups. I'm thinking you want the pH at which is is no longer ionized. I'm headed home, but you might try searching with the terms ionization and/or pKa. With the sulfate groups, it is going to be low.

 

[Kaiser]

Also found this in a book. It says that carrageenan is strongly negatively charged over the entire pH-range encountered in food.
Nice tidbits in a marine book

Good enough, Thanks.

I needed the IEP to determine the range over which carrageen is negatively charged.

Kai

 

[Kaiser]

Also found this in a book. It says that carrageenan is strongly negatively charged over the entire pH-range encountered in food.
Nice tidbits in a marine book

I thought about this some more and maybe we can have a good discussion about this here:

I think Irish Moss shouldn’t work as well as it does if it is negatively charged during the boil.

In this book http://books.google.com/books?id=TQuwGXt2NYAC&pg=PR11&dq=biotechnology+malting+brewing#v=onepage&q=when%20analysed%20the%20protein%20precursor&f=false

it states that the IEP of haze proteins is between 3 and 5.5 and the IEP of foam proteins is between 5.5 and 8. At a pH below its IEP a molecule is predominately positively charged and above its IEP it is predominately negatively charged.

This means at a boil pH of 5-5.3 most of the haze proteins are above their IEP and therefore negatively charged. The foam proteins however are positively charged. Irish Moss is added to precipitate the haze proteins and for this it needs to be positively charged. If it was negatively charged it would attract the foam proteins which is not desired.

The whole thing works for gelatin which has an IEP of 4.85 or ~7.0-9.0 and is positively charged at beer pH (4.0-4.5) where it is used.

Here is something I found on BYO.com (http://www.byo.com/stories/techniques/article/indices/23-clarity/490-conquer-chill-haze)

The active ingredient in Irish moss is carrageen, which is used in many food products as well as in beer. Carrageen has a natural negative electrical charge, and the protein particles in boiling beer wort have a positive electrical charge. When they encounter each other in boiling beer wort, they stick together. And since the Irish moss is very heavy, it helps to drop these compounds out during wort chilling. One-half teaspoon of Irish moss should be added to every five-gallon batch of beer 15 minutes before the end of the boil. Avoid chill haze by serving beer around 55° F.

Kai

 

[pjj2ba]

I believe it is not just the negative charges that do the job. I think of them merely as a great starting point - getting the snowball rolling. Once you've got some positively charged proteins attracted to the carrageenan, things start to get complex. I think the use of predominantly is key. Even above an IEP, there will still be enough positively charged Amino Acid residues (even if for just a split second) on the peptides for some binding to occur - just slower. Once it starts to grow, now you'll start getting hydrophobic AA residues to start interacting with one another, plus other intermolecular forces attracting other proteins. It's not just the carrageenan doing the work, it is all of the other proteins that get stuck on, and their own unique affinity for other peptides. I don't think there is a defined amount of peptides that a given amount of carrageenan will precipitate. It is going to very from liquid to liquid, depending on the components.

 

[Kaiser]

My problem with this is that the book that I listed above states that proteins responsible for head retention have IEP higher than the boil pH and therefore will carry a net positive charge which would make them more likely to be attracted by the Irish Moss than the haze proteins. As a result, beers treated with Irish Moss in the kettle should have a lower head retention which has not been seen.

Another possibility is that that statement of the different IEP ranges for haze and head retention proteins is not correct.

On a different note, does someone know if Knox unflavored Gelatin is made from prok or from cow? It makes a different in its IEP.

Kai

 

[Kaiser]

Here is something I found in Brigg’s Brewing Science and Practice regarding the use of Irish Moss:

“A wort pH of 5.0 is required for efficient fining and worts below pH 4.5 often fail to fine”. It also states that Irish Moss is negatively charged

If we want to explain the workings of Irish Moss through attraction of negatively and positively charged molecules, we above statement doesn’t make sense. As the pH falls, the charge of the protein has to become more positive. I.e. it would be even more attracted to the negatively charged Irish Moss.

Kai

 

[pjj2ba]

I guess two things that come to my mind are what is the role of the yeast in producing foam positive proteins - or in other words, while some foam positive proteins may be lost by using irish moss, new ones are created (or modified) during fermentation.

The other thing is what is the relative abundance of the haze proteins versus the foam proteins. Maybe there is a lot more of the foam proteins so the loss of a small bit might not be so noticible, but enough of the haze proteins have been removed at the same time.

Back to the first point. It has been my observation (anecdotal) that the longer a beer has been on tap (~42 F) the better the head retention. This might indicate a role for yeast (of course it doesn't rule out strictly chemical reactions)

 

[PseudoChef]

I'm late to the party, but looking up on Expasy, the theoretical pI of mastocarpus stellatus (the only full length sequence I could find) is 5.7.

 

[bad coffee]

I don't know if this helps you Kai, it might be a little less scientific than you're looking for.

http://www.brewerssupplygroup.com/pdf/knowledge_center/WortandBeerFining_Manual.pdf

B